Gels are macromolecules cross-linked by chemical or physical fastenings forming a polymer network that is highly swollen by a solvent. Normally the mass of the absorbed solvent heavily exceeds the mass of the polymer network. When gels are applied to surfaces, adhesive bonds form due to the intermolecular attraction between unlike molecules, such as those in a gel and in a surface. Each bond may be characterized by adhesion strength which is equal to the disbonding force divided by the bond area.
The adhesion strength of such a bond may vary from high to very low depending on the level of gel-surface interaction. If adhesion-control tools are available, i.e., modalities capable of increasing the adhesion of gels naturally having a low adhesion strength and capable of decreasing the adhesion of gels naturally having a high adhesion strength, the range of applications of the given system is much broader and much more desirable.
Another desirable feature of adhesion control is reversible and repeatable adhesion, e.g. adhesion of the given gel-surface interface can be increased or decreased within a range of naturally possible adhesion strengths. Reversible and repeatable adhesion provides a solution for the long-standing problem of achieving the correct balance between a tight seal and an easy peel of gel-forming polymeric materials.
The adhesion strength of a material can be controlled using several methods. For example, certain control methods are described in U.S. Pat. No. 4,985,274 and U.S. Pat. No. 6,546,624.
U.S. Pat. No. 4,985,274 relates to a method for preparing pressure sensitive adhesives in which the release force of the adhesive can be controlled by controlling the amount of oxygen introduced that is reactive with the release coating.
U.S. Pat. No. 6,546,624 relates to a process including a removable film having removability wherein said removability enables the film to be removed from a substrate after the film is drilled by laser light along with the substrate.
However, an effective tool for adhesion control is an electric field; an electric field may be used for incorporating or contacting materials.
For example, U.S. Pat. No. 5,552,012 concerns a manner for incorporating a material responsive to an electric field into an absorbent structure, wherein the material responsive to an electric field remains substantially neutrally charged during the process. The absorbent structure is prepared by a known process comprising using an electric field to contact a material responsive to an electric field, selected from the group consisting of a hydrogel-forming polymeric material and an adhesive material, with a substrate, wherein the material responsive to an electric field remains substantially neutrally charged during the process.
In U.S. Pat. No. 4,900,387, the electroreological material increases and maintains the viscosity of the adhesive in a nonflowable, gel-state when an electric field is applied, and keeps it from running.
An electric field may also be used for paint removal from a substrate. U.S. Pat. No. 5,507,926 is directed to a method of electrolytically separating a paint coating from a metal surface comprising the steps of providing a metal member having a surface having a paint coating thereon and contacting the member with an essentially neutral electrolytic solution. The metal member is made cathodic in an electrolytic cell and current is passed from an anode through the electrolytic solution to the metal member for a time sufficient to cause the paint coating to separate from the metal member.
U.S. Pat. No. 6,030,519 also relates to paint removal from metal members such as metal parts, objects and structures and more particularly. It relates to an anode electrode pad for electrolytically assisted removal of paint from large structures such as bridge structures, tanks, ships, airplanes, automobiles and the like. This method of electrolytically separating a paint coating from a metal surface comprising the steps of providing a metal member having a surface having a paint coating thereon and contacting the member with an essentially neutral electrolytic solution. The metal member is made cathodic in an electrolytic cell and current is passed from an anode electrode pad through the electrolytic solution to the metal member for a time sufficient to cause the paint coating to separate from the metal member.
U.S. Patent Application Publication No. 20010031367 discusses an electrochemically disbondable composition having a matrix functionality and an electrolyte functionality, wherein the electrolyte functionality may be provided by a block copolymer or a graft copolymer. The matrix functionality provides an adhesive bond to a substrate, and the electrolyte functionality provides sufficient ionic conductivity to the composition to support a faradic reaction at an interface with an electrically conductive surface in contact with the composition, whereby the adhesive bond is weakened at the interface. The composition may be a phase-separated composition having first regions of substantially matrix functionality and second regions of substantially electrolyte functionality. Adhesive and coating compositions and methods of disbonding also are described. A bonded joint may be obtained by applying an adhesive of the invention to a suitable surface as a solution, a melt or a reactive mixture. Solvents, if used, may be removed by evaporation prior to mating the substrates, or may be absorbed by the coated substrate. Compositions applied as a melt, a solution, or a reactive mixture wet the substrates, and then solidify, in order to achieve a high level of adhesion.
U.S. Patent Application Publication No. 20040256246 discloses a method of electrolytically debonding a paint coating from an electrically nonconductive member wherein the paint coating is bonded to a surface of the nonconductive member. The method comprises providing an electrode blanket on the paint coating, the electrode blanket comprised of a first blanket layer in contact with the paint coating, a negative electrode layer in contact with the first blanket layer, a second blanket layer covering the negative electrode layer, a positive electrode layer in contact with the second blanket layer, and a third blanket layer covering the positive electrode layer. An aqueous-based electrolyte solution is applied to the electrode blanket. An electric current is passed from the negative electrode to the positive electrode, evolving hydrogen at the negative electrode, thus creating an alkaline condition thereby causing delamination and degrading of the paint coating on the electrically nonconductive member. Solvent is not used as a component of the removable material discussed in the U.S. Patent Application Publications No. 20010031367 and No. 20040256246. By the testing time the discussed materials are solvent-free. However, the presence of a solvent can be a factor influencing debonding properties of materials under an electric field effect. The gel-like materials are solvent-containing materials.
U.S. Pat. No. 6,027,075 concerns a system that can be used to modify ice adhesion strength of ice adhered to an object. The system includes an electrode that is electrically insulated from the object and a DC source, e.g., a battery, coupled to the object and the electrode. The source generates a DC bias to an interface between the ice and the object when the ice completes the circuit. The object is conductive or is doped as a semiconductor so that the DC bias applies a voltage to the interface which modifies the ice adhesion strength selectively as compared to the ice adhesion strength with substantially zero bias voltage at the interface. The strength can be increased or decreased relative to its static state (i.e., the state without applied voltage). In this manner, ice such as ice on an aircraft wing can be removed with less work. The system preferably includes an electrically insulating material disposed between the object and the electrode; the insulating material is substantially conformal to the object and the electrode. In most applications, the electrode includes a grid electrode shaped to conform to a surface of the object and each point of the grid electrode is in electrical contact with the source. Accordingly, a grid insulator is generally disposed between the object and the grid electrode. The system has high applicability to objects such as an aircraft wing, an automobile windshield, a bottom of a ski, a heel or sole or a boot or shoe, and an outer material of a power line. The system also includes a ferroelectric, ferromagnetic or semiconductor coating applied to power lines to auto-regulate the temperature of the lines to just above the melting point.
However, prior to the instant invention, there was no recognition of the use of an electric field usage for the bonding control of polymer gels. Such control is very desirable, since adhesive gels can be repeatedly applied to a surface if they can be removed without structural damage. Effective methods for adhesion control of polymer gels can therefore improve the quality of applications of removable adhesive materials.